An oily ink, hereinafter may simply be referred to as “ink”, has advantages that it does not cause curling of printing paper, and that it allows a shorter period of drying time. However, it shows a problem of so-called “strike-through” of the ink caused by a pigment penetrate into paper together with a solvent, reducing density of printed images.
To solve this problem, the patent publication 1 proposes a method of incorporating inorganic fine particles in an oily ink to fill pores of paper by the inorganic fine particles, and the patent publication 2 proposes a method of dispersing a resin having a polar group in a non-aqueous solvent. However, in the former method, the effect of filling pores of paper is limited because the fine particles should have such a particle size that they do not plug a nozzle of an inkjet head. The latter method requires preparing the specific resin.
Meanwhile, an inkjet ink comprising resin particles in a non-aqueous solvent is known from the patent publication 3. The resin forms a film in a process of drying at a temperature of 120° C. to encapsulate pigments, resulting in an improved fixing and weather resistance of the ink. However, a satisfactory prevention of strike-through is not achieved.